The present invention relates to a fluid actuated cylinder and more particularly to a fluid actuated cylinder which is adaptable for use in a linkage system that may be subjected to a side loading in addition to a desired axial loading.
In the field of fluid cylinder construction, many devices exist which are employed to provide axial loading in a linkage arrangement through the use of liquid or hydraulic power, and many of the designs presently in use have been employed with success over a period of years. However, there exists a problem in the design of such devices which in some instances can lead to failure and may, in any event, lead to the shortening of the useable life of the device.
In most designs of this type, a single nose bearing is employed to support the piston rod at the nose end of the cylinder and the bearing length is rarely longer than twice, and usually less than one and a half times the diameter of the piston rod. This is largely due to the mounting and interchangability standards of the industry that more or less dictate the configuration of the mounting centers, diameters, lengths, shoulder positions, port sizes, etc. When a cylinder such as this is used in an application where the load or resisting forces are closely coaxial with the centerline of the piston rod assembly, the length to diameter ratio on the nose bearing is not of great importance to longevity, reliability, etc. In addition, a cylinder with a primarily axial load is usually mounted at the nose end and located in the linkage wherein side loads and reverse loading are not of importance, although situations may arise where users apply side loading and reverse loading to nose mounted cylinders of this type.
On the other hand, when a cylinder is employed as part of a rocking linkage for example, it is mounted by a pivot pin at the tail portion of the cylinder, a clevis is screwed onto the threaded end of the rod which in turn is freely pinned to a bell crank or link. With this type of linkage, there is a side load condition present at the nose bearing which is induced by the weight of the cylinder tending to cause the assembly to sag due to the spacing provided in the manufacturing clearance of the nose joint bearing. Thus this sag induces, for example, a side load on the nose bearing. Further, when the cylinder is actuated by the fluid entering a port, the resulting forces (including reaction forces) acting upon this sliding nose joint causes the rod to tilt in the opposite extreme as it translates through the bearing in the process of applying force to the driven load or in the process of retraction.
During operation, this loading induces a tilting effect of the rod through the nose bearing which takes place in the slight clearance provided in the manufacturing process and as the rod extends, the rocking effect of the applied load by the bell crank causes this tilting to reverse to the opposite extreme. In some applications the reversal is sudden, possibly creating shock loading. This reversal of loading on the nose bearing very rapidly induces wear at the inner and outer edges of the bearing bore and these repeated reversals of loading lead to accelerated wear and early malfunction and/or failure. Typically, the piston outer diameter which has a much greater clearance to the wall than is customary in the bearings, soon rubs or drags on the cylinder wall creating excessive forces which must be overcome and which create a generally unacceptable resistance to motion within the cylinder.
In conventional designs, the inner and outer edges of the nose bearing absorb the reaction force while simultaneously being subjected to highly concentrated loading. The present invention spreads this force couple substantially equally between the two separate bearings thereby to reduce the load concentrations substantially and thereby increase the life of the bearing surfaces as well.
Exemplary of the prior art are pistons disclosed in the following patents:
______________________________________ Cole 1,003,235 Beckett 3,180,236 Jacobsen 1,598,138 Paul 3,717,070 Braren 1,747,968 Ides 4,185,543 Christensen 2,410,808 Wallischeck 4,211,151 Shepherd 3,132,569 Devaud 4,414,881 Renzi 4,592,267 Dirkin 4,685,384 ______________________________________
The present invention therefore has an object to provide a fluid actuated cylinder which retains its operating integrity and efficiency when incorporated into a linkage which is susceptible to side loading.
A further object of the invention is to provide a fluid actuated cylinder of the type described which retains its operating integrity and efficiency under side loading while staying substantially within the industry's standards of mountings, length, diameter, ports, etc.
Another object of the invention is to provide a fluid actuated cylinder which retains the convenience and feature of a pivot mounting hole in the tail sub-assembly while displaying a high degree of efficiency and integrity when employed in a linkage which may be susceptible to side loading.
Yet another object of the invention is to provide a fluid actuated cylinder of the type disclosed which can readily be employed to update, rebuild or repair, machinery presently in use, the cylinder having mounting characteristics which are substantially the same as products which were provided in the past.
Still a further object of the invention is to provide a fluid actuated cylinder which has a minimum number of components, all of which are readily accessible for repair or replacement, during the life of the cylinder.